Question 1

What is linear momentum and why is it important in physics?

Accepted Answer

Linear momentum is a vector quantity representing an object's 'quantity of motion', defined as the product of its mass and velocity ($p = mv$). It's crucial because it allows us to analyse interactions like collisions and explosions, especially through the Principle of Conservation of Momentum, which predicts outcomes when forces are internal to a system.

Question 2

Under what conditions is linear momentum conserved?

Accepted Answer

Linear momentum is conserved in a closed system, meaning no mass or energy enters or leaves. Crucially, it is conserved only when the net external force acting on the system is zero. Internal forces (like the forces of collision between objects) do not change the total momentum of the system.

Question 3

How can you tell if a collision is elastic or inelastic?

Accepted Answer

You can distinguish between elastic and inelastic collisions by examining the total kinetic energy of the system. In an *elastic* collision, the total kinetic energy before the impact is equal to the total kinetic energy after. In an *inelastic* collision, the total kinetic energy is not conserved; some of it is transformed into other forms like heat, sound, or energy used for deformation, making the final kinetic energy less than the initial.

Question 4

What is the relationship between force and impulse?

Accepted Answer

Force is the rate of change of momentum ($F = \Delta p / \Delta t$). Impulse is the total change in momentum ($J = \Delta p$). Therefore, impulse is also equal to the average force multiplied by the time it acts ($J = F \Delta t$). A large impulse can be delivered by a large force over a short time, or a smaller force over a long time.

Linear momentum and its conservation

What you need to know

Linear momentum and its conservation